全文获取类型
收费全文 | 176836篇 |
免费 | 10309篇 |
国内免费 | 5234篇 |
专业分类
电工技术 | 7204篇 |
技术理论 | 3篇 |
综合类 | 8869篇 |
化学工业 | 26180篇 |
金属工艺 | 10257篇 |
机械仪表 | 9447篇 |
建筑科学 | 9329篇 |
矿业工程 | 3849篇 |
能源动力 | 3653篇 |
轻工业 | 10175篇 |
水利工程 | 3096篇 |
石油天然气 | 5443篇 |
武器工业 | 921篇 |
无线电 | 20690篇 |
一般工业技术 | 26743篇 |
冶金工业 | 6650篇 |
原子能技术 | 1266篇 |
自动化技术 | 38604篇 |
出版年
2024年 | 448篇 |
2023年 | 1638篇 |
2022年 | 2967篇 |
2021年 | 4164篇 |
2020年 | 3198篇 |
2019年 | 2672篇 |
2018年 | 17020篇 |
2017年 | 16397篇 |
2016年 | 12754篇 |
2015年 | 4907篇 |
2014年 | 5436篇 |
2013年 | 6208篇 |
2012年 | 9868篇 |
2011年 | 16513篇 |
2010年 | 14298篇 |
2009年 | 11155篇 |
2008年 | 12145篇 |
2007年 | 12894篇 |
2006年 | 5530篇 |
2005年 | 5631篇 |
2004年 | 4240篇 |
2003年 | 3597篇 |
2002年 | 2682篇 |
2001年 | 1993篇 |
2000年 | 2125篇 |
1999年 | 2036篇 |
1998年 | 1738篇 |
1997年 | 1438篇 |
1996年 | 1333篇 |
1995年 | 1072篇 |
1994年 | 914篇 |
1993年 | 633篇 |
1992年 | 501篇 |
1991年 | 424篇 |
1990年 | 283篇 |
1989年 | 250篇 |
1988年 | 202篇 |
1987年 | 118篇 |
1986年 | 93篇 |
1985年 | 60篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 43篇 |
1965年 | 45篇 |
1959年 | 39篇 |
1958年 | 38篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
981.
甲醇与碳酸二甲酯共沸液的分离研究进展 总被引:8,自引:0,他引:8
综述了DMC-CH_3OH二元共沸液的各种分离方法。讨论了共沸精馏和萃取精馏的工艺流程。 相似文献
982.
983.
984.
固体碱催化戊醛缩合的研究 总被引:4,自引:0,他引:4
韩非 《精细石油化工进展》2003,4(11):25-27
自制了固体碱催化剂用于催化戊醛缩合反应 ,考察了碱金属、载体、反应温度、反应压力、空速等条件对反应的影响。研究表明 ,以介孔分子筛为载体的催化剂活性尤其是低温活性明显高于以硅胶为载体的催化剂。自制的固体碱催化剂性能稳定 ,在 2 0MPa ,2 60℃ ,1 0h-1条件下连续运转 2 7d,仍能保持转化率高于 90 %、选择性约 80 %的良好效果。 相似文献
985.
本文主要讲述如何利用Cache技术,来有效的提高网站性能。以ASP.NET为基础,展示ASP.NET中使用Cache的新特性,主要应用了Databasedependencies技术。 相似文献
986.
987.
Possibilities and problems with the use of models as a communication tool in water resource management 总被引:2,自引:1,他引:1
Politicians and policy-makers, as well as modellers, often nurses an expectation that model derived results is an objective
source of information that can be used to support decisions. However, several prerequisites have to be dealt with in order
to ensure that models can be used as legitimate and efficient tools in water resource management. Based on empirical material
from recent studies on the use of models in stakeholder dialogues, mainly focusing on catchment nutrient transport, two central
problems are identified: (a) Models are laden with choices and thus depend on assumptions and priorities of modellers. (b)
There are several factors that influence ability and willingness of stakeholders (as information recovers) to criticize or
accept results of the modelling exercise. Recognized factors likely to influence stakeholders' acceptance of model derived
results include issues at stake, stakeholders' ability to criticize model derived information, and their trust in the institutions
that have developed or applied the used models. Identified prerequisites for successful use of models in integrated water
resource management include: consideration of user relevance, awareness of and preparedness to handle constraints linked to
communication of model-based results, transparency of used models and data and of involved uncertainties, mutual respect between
experts and stakeholders and between involved stakeholder groups, a robust institutional network, and sufficient time for
dialogues. Development and use of strategies for participatory modelling, based on a continuous dialogue between experts and
stakeholders is recommended as a way to facilitate that the prerequisites for a successful use of models in water resource
management are fulfilled. 相似文献
988.
989.
Jeongbae Kim Hee Youl Kwak Dong Won Lee 《Journal of Mechanical Science and Technology》2007,21(12):2159-2167
In this study, we highlighted differences in the standards used in performance tests of solar collectors. We analyzed testing
results for different types of solar collectors to determine the effects of the collector area and mass flow rate, which were
not necessarily consistent across all tests. Our analysis showed that the factor,F′ (τα), including collector efficiency factor (F′), could be correlated with the flow rate or area regardless of the collector type. Moreover, the collector loss coefficient
(F′U
L
) per flow rate or area for an evacuated collector was less that of a flat-plate collector; this was also correlated with
the flow rate or area, regardless of the type of evacuated collector. As a result of this analysis, we propose a modified
heat loss coefficient that includes the effects of all parameters that can be considered in a performance test and show that
this coefficient could better describe the thermal characteristics of various types of solar collectors. 相似文献
990.
Polydorou and Capsalis [1] pioneered the concept of POCA distribution to study the statistical behavior of the fast fading characteristics in an indoor environment under the assumption of finite
number of scatters. In this note, we derive a comprehensive class of formulas for the POCA distribution to help better statistical modeling of the fast fading characteristics. The calculations involve use of several special functions
and their properties. 相似文献